Basic Principles of Signal Integrity

Digital designs have not traditionally suffered from issues associated with transmission line effects. At lower frequencies the signals remain within data characterization and systems perform as designed. But as system speeds increase, the higher frequency impact on a system means that not only the digital properties, but also the analog effects within the system, must be considered. These problems are likely to come to the forefront with increasing data rates for both I/O interfaces and memory interfaces, but particularly with the high-speed transceiver technology being embedded into FPGAs. As speed increases, high-frequency effects take over and even the shortest lines can suffer from problems such as ringing, crosstalk, reflections, and ground bounce, seriously hampering the integrity of the signal. This application note describes how these issues can be resolved with sound design techniques and simple layout guidelines.